Bonded joints can be used in order to produce a connection between two elements or components, for example of a vehicle. Here, a distinction is made between primarily bonded joints, in which the bonding process is carried out over the period of time in which the two elements are also shaped (for example in a press), and secondarily bonded joints, in which the components are bonded to one another subsequently.
In the case of a bonded joint of a supporting structural element, it may be important to check for operation-induced damage. Most bonded joints are no longer accessible from all sides following the joining and assembly to form the overall structure, and therefore can no longer be examined well by visual inspection.
In aviation, secondarily bonded joints currently are not admissible, since it generally is not possible to easily check whether or not a secondarily bonded joint is damaged.
Known methods for the non-destructive testing of bonded joints include, for example, ultrasound and thermography. However, these methods can be applied only to a limited extent or can be used only with difficulty in the case of large wall thicknesses or thickness changes of the glue line.
In the case of a faulty bonding as well, in which only under load is a gap produced between the components no longer correctly bonded (what are known as kissing bonds), it is often not possible to discover any faults using the above-mentioned methods.
For these reasons additional clamping bolts are often used with bonded joints. The bolts are designed to carry the load of the joint when the bonded joint is damaged. Such clamping bolts may then delay a further spread of damage, but may also prevent detection of the damage.